feat: add floor themes with status effect modifiers

Add 4 floor themes (Swamp/Volcano/Glacier/Inferno) that boost status
effect damage on matching floors. Realign boss patterns to match themes
and add PatternFreeze for the Glacier boss.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

dungeon/theme.go

@@ -0,0 +1,32 @@
+package dungeon
+
+import "github.com/tolelom/catacombs/entity"
+
+// ThemeModifier defines gameplay modifiers for a range of floors.
+type ThemeModifier struct {
+	Name        string
+	StatusBoost entity.StatusEffect // which status is boosted (-1 = all for Inferno)
+	DamageMult  float64
+	Description string
+}
+
+var themeModifiers = []ThemeModifier{
+	{"Swamp", entity.StatusPoison, 1.5, "Toxic marshes amplify poison"},
+	{"Volcano", entity.StatusBurn, 1.5, "Volcanic heat intensifies burns"},
+	{"Glacier", entity.StatusFreeze, 1.5, "Glacial cold strengthens frost"},
+	{"Inferno", entity.StatusEffect(-1), 1.3, "Hellfire empowers all afflictions"},
+}
+
+// GetTheme returns the theme modifier for the given floor number.
+func GetTheme(floor int) ThemeModifier {
+	switch {
+	case floor <= 5:
+		return themeModifiers[0]
+	case floor <= 10:
+		return themeModifiers[1]
+	case floor <= 15:
+		return themeModifiers[2]
+	default:
+		return themeModifiers[3]
+	}
+}

dungeon/theme_test.go

@@ -0,0 +1,32 @@
+package dungeon
+
+import "testing"
+
+func TestGetTheme(t *testing.T) {
+	tests := []struct {
+		floor int
+		name  string
+	}{
+		{1, "Swamp"}, {5, "Swamp"},
+		{6, "Volcano"}, {10, "Volcano"},
+		{11, "Glacier"}, {15, "Glacier"},
+		{16, "Inferno"}, {20, "Inferno"},
+	}
+	for _, tt := range tests {
+		theme := GetTheme(tt.floor)
+		if theme.Name != tt.name {
+			t.Errorf("floor %d: expected %q, got %q", tt.floor, tt.name, theme.Name)
+		}
+	}
+}
+
+func TestThemeDamageMult(t *testing.T) {
+	theme := GetTheme(1) // Swamp
+	if theme.DamageMult != 1.5 {
+		t.Errorf("Swamp DamageMult: expected 1.5, got %f", theme.DamageMult)
+	}
+	theme = GetTheme(20) // Inferno
+	if theme.DamageMult != 1.3 {
+		t.Errorf("Inferno DamageMult: expected 1.3, got %f", theme.DamageMult)
+	}
+}

entity/monster.go

@@ -41,6 +41,7 @@ const (
 	PatternPoison              // applies poison
 	PatternBurn                // applies burn to random player
 	PatternHeal                // heals self
+	PatternFreeze              // applies freeze to all players
 )
 
 type Monster struct {

game/event.go

@@ -119,13 +119,13 @@ func (s *GameSession) spawnBoss() {
 	boss := entity.NewMonster(mt, s.state.FloorNum, s.cfg.Combat.MonsterScaling)
 	switch mt {
 	case entity.MonsterBoss5:
-		boss.Pattern = entity.PatternAoE
+		boss.Pattern = entity.PatternPoison // Swamp theme
 	case entity.MonsterBoss10:
-		boss.Pattern = entity.PatternPoison
+		boss.Pattern = entity.PatternBurn // Volcano theme
 	case entity.MonsterBoss15:
-		boss.Pattern = entity.PatternBurn
+		boss.Pattern = entity.PatternFreeze // Glacier theme
 	case entity.MonsterBoss20:
-		boss.Pattern = entity.PatternHeal
+		boss.Pattern = entity.PatternHeal // Inferno theme (+ natural AoE every 3 turns)
 	}
 	if s.state.SoloMode {
 		boss.HP = int(float64(boss.HP) * s.cfg.Combat.SoloHPReduction)

game/turn.go

@@ -72,13 +72,30 @@ collecting:
 }
 
 func (s *GameSession) resolvePlayerActions() {
-	// Tick status effects
+	// Tick status effects with floor theme damage bonus
+	theme := dungeon.GetTheme(s.state.FloorNum)
 	for _, p := range s.state.Players {
 		if !p.IsOut() {
+			// Snapshot effects before tick to compute theme bonus
+			effectsBefore := make([]entity.ActiveEffect, len(p.Effects))
+			copy(effectsBefore, p.Effects)
+
 			msgs := p.TickEffects()
 			for _, msg := range msgs {
 				s.addLog(msg)
 			}
+
+			// Apply theme damage bonus for matching status effects
+			for _, e := range effectsBefore {
+				if e.Value > 0 && (theme.StatusBoost == entity.StatusEffect(-1) || e.Type == theme.StatusBoost) {
+					bonus := int(float64(e.Value) * (theme.DamageMult - 1.0))
+					if bonus > 0 {
+						p.TakeDamage(bonus)
+						s.addLog(fmt.Sprintf("  (%s theme: +%d damage)", theme.Name, bonus))
+					}
+				}
+			}
+
 			if p.IsDead() {
 				s.addLog(fmt.Sprintf("☠ %s has fallen!", p.Name))
 			}
@@ -409,6 +426,13 @@ func (s *GameSession) resolveMonsterActions() {
 							s.addLog(fmt.Sprintf("%s burns %s!", m.Name, p.Name))
 						}
 					}
+				case entity.PatternFreeze:
+					for _, p := range s.state.Players {
+						if !p.IsOut() {
+							p.AddEffect(entity.ActiveEffect{Type: entity.StatusFreeze, Duration: 1, Value: 0})
+							s.addLog(fmt.Sprintf("%s freezes %s!", m.Name, p.Name))
+						}
+					}
 				case entity.PatternHeal:
 					healAmt := m.MaxHP / 10
 					m.HP += healAmt